Conventional organic solvent based polymer compositions have become disfavored due to problems associated with environmental pollution, conservation of resources and providing a safe working environment. Instead, aqueous solution or dispersion type polymer compositions and high solids or 100 active polymer compositions have been proposed as alternatives. These alternative polymer compositions eliminate many of the problems associated with the evaporations of large amounts of organic solvents during the cure of low solids, organic solvent based polymer compositions. Much attention has been paid to reactive polymer emulsions and dispersions because of the ease with which they provide improved properties such as water and solvent resistance.
The use of combinations of polymers, aqueous emulsions and dispersions (lattices) and epoxy resins or compounds is well known in the art. For example, U.S. Pat. No. 4,049,869 to Long taught a composition including a high acid acrylic latex (5 to 20% by weight), a crosslinking agent (1 to 10%) and an ultraviolet absorber for use in preserving porous inorganic substrates. The crosslinking agent can include an epoxy resin.
Water-soluble silanes as additives in latex systems have also been disclosed in the prior art. For example, U.S. Pat. No. 5,017,632 to Bredow disclosed coating compositions for Portland cement or metal. The coating composition thereof can be mixed from a pair of storage stable components; a dry mix including a fine particle size filler, an epoxy resin and optionally, a course aggregate, and a wet mix including a polymer latex, an amine-functional epoxy curing agent, and a water-soluble epoxy or amino-silane.
U.S. Pat. No. 5,100,955 to Pons disclosed coating and adhesive compositions based on aqueous dispersions of addition polymers of one or more olefinically unsaturated monomers, emulsion stabilizers and/or emulsifiers and a water-soluble epoxysilane. The water-soluble epoxysilane is added preferably after the polymerization of the addition polymer. The shelf-life, however, of such,compositions is only from two to three days.
EP Patent No. 401,496 to Hahn disclosed aqueous silicon-modified plastic dispersion as adhesives by epoxysilane-treatment of a dispersion of emulsion copolymers containing carboxylic acid, amide and sulfonic acid groups. Water soluble epoxysilanes of the formula R1R2R3R4Si are disclosed with R1=(cyclo)alkyl with reactive oxirane group; R2=(cyclo)alkoxy, (cylco)alkyl, aryl or aralkyl; R3, R4=(cyclo)alkoxy, or OH. However, the composition of the synthetic latex is specific. Furthermore, the neat epoxysilane is added directly to the polymer.
In addition to these coating technologies, emulsions of trialkoxysilanes have been previously reported as waterproofing agents. For example, buffered aqueous silane emulsions are disclosed in U.S. Pat. Nos. 4,877,654 and 5,393,330. Alkylalkoxysilanes are also emulsified with nonionic and anionic emulsifiers for water repellency properties in U.S. Pat. No. 5,226,954.
High solids or 100 percent actives reactive epoxy compositions also eliminate or reduce the-problems associated with the organic solvent based polymer compositions. Many of these epoxy compositions involve the reaction of epoxies with organic acids.
The broader use of these reactive epoxy compositions has been constrained because these epoxy compositions require high temperatures and/or long times to force the reaction of the epoxies with the organic acids. Heterogeneous and homogeneous catalysts have been used to promote the reactions between epoxides and organic acids. Sulfuric acid, p-toluene sulfonic acid, phosphomolybdic acid, boron triflouride, sodium alkoxide, alumina, ceric (IV) ammonium nitrate and photolytically generated superacids have been evaluated as catalysts for the reaction of cycloaliphatic epoxides with organic acids (S. Wu and M. D. Soucek, Polymer, 39 (23), 5747, 1998 and references cited herein). N. Iranpoor and B. Zeynizadeh found that bis-(trifluoroacetic) titanium oxide and trichlorotitanium triflate promoted the reaction of epoxy compounds (Synthetic Communications, 29 (6), 1017, 1999). However, many of these catalysts promote undesirable side reactions, such as the homopolymerization of the epoxy group, or are corrosive with many substrates.
M. Caron and K. B. Sharpless have shown that 2,3-epoxy compounds containing a titanate group were reactive with organic acids (Journal of Organic Chemistry, 50, 1557, 1985). The 2,3-epoxy compounds were made by reacting 3-propyloxiranemethanol with a stoichiometric amount of tetraisopropyl titanate. However, no epoxy ring opening reaction was found if a stoichiometric amount of methyl 3-propyloxirane methyl ether was mixed with tetraisopropyl titanate in the presence of amines. The methyl group on the ether blocked the formation of the 3-propyloxiranemethyl tri-isopropoxy titanate compound. These observations indicate that tetraisopropyl titanate is not a catalyst for the reaction of nucleophiles with epoxy compounds, unless the epoxy compound has a hydroxy group alpha to the oxirane group.
A need therefore exists for improved catalysts to facilitate the reaction of epoxies with organic acids.
The present invention is directed to reactive epoxy compositions employing select curing catalysts. The invention in this regard advantageously contemplates epoxy compounds that either contain silane groups (epoxysilane) or not (non-silane epoxy compound).
In a first practice of the present invention, the composition comprises a water insoluble or slightly soluble epoxysilane and/or a non-silane epoxy compound; an emulsifier; water; a compound containing at least one carboxylic acid group; and a curing catalyst selected from the group consisting of a chelated Ti(IV) compound and a chelated Sn(II) compound.
In a second practice of the invention, the composition comprises an epoxysilane and/or a non-silane epoxy compound; a compound containing at least one carboxylic acid group; and a curing catalyst selected from the group consisting of a unidentate Ti(IV) compound, a chelated Ti(IV) compound, a unidentate Sn(II) compound and a chelated Sn(II) compound, the composition being substantially free of water.
Another aspect of the present invention is to provide an article coated and cured with any of the aforementioned reactive compositions.
The compositions of the present invention offer improved properties such as solvent resistance, adhesion, smoothness, hardness and mar resistance.